A. Field of the Invention
The present invention relates generally to a seismic gun assembly having a guide tube for delivering a projectile through a bore hole to interact with geologic formations. Additionally, the present invention relates to an assembly for suppressing noise when introducing a projectile through a guide tube, a fluid preventative seal for preventing fluids from entering the guide tube, and a method and apparatus for modulating the recoil force when the seismic gun is fired.
B. Background of the Invention
Seismic apparatuses and seismic guns are presently used as a tool for acquisition of data on geographical topology. Geographical survey specialists use seismic guns that launch projectiles into bore holes to create seismic waves which return data on underground topology. Presently, these seismic guns do not produce accurate data because of their inability to launch projectiles to the bottom of non-line-of-sight bore holes.
Another difficulty with obtaining geological topology data from the use of seismic guns is the collection of natural water in reservoirs. The energy of pressure waves caused by the impact of the projectile at the bottom of the bore hole depends upon the momentum the projectile transfers when it impacts the ground. Stronger pressure waves provide more reliable data. When a projectile passes through a fluid, the momentum of the projectile is reduced before reaching the end of the bore hole and thus the magnitude of the impact at the end of the bore hole is reduced. Hence, the relevant pressure waves are weaker and the received data is less accurate.
Currently, seismic exploration of geophysical material begins with use of a rotary drilling rig, which drills intermediate depth holes in the ground for the insertion of a seismic gun barrel. It is well known in the relevant art that over long distances a rotary drill will deviate from a straight-line course and produce a vertical bore hole that does not have a linear line-of-sight from the top to the bottom of the bore hole. Present seismic guns fail to account for bore holes that are non-line-of-sight. As a consequence, the projectiles of current seismic guns typically contact the sides of the bore hole before reaching the bottom. This causes two problems, first the projectile loses momentum before reaching the bottom of the bore hole; and second, the contact with the side of the bore hole causes extraneous pressure waves which may interfere with sensors that detect reflected pressure waves.
Moreover, launching of projectiles via chemical propellants or compressed gas may cause loud noises to be emitted in the surveyed area. Noise pollution of this type has two distinct problems. First, the noise may create additional pressure waves which will interfere with the sensors. Second, the noise may be dangerous to workers and a nuisance to people nearby.
Lastly, there exists a problem relating to the recoil of seismic guns when the projectile is launched from the surface into the bore hole. The force used to launch a projectile at a preferred velocity will be of such a magnitude that it will cause the seismic gun to recoil strongly in the opposite direction in which the projectile is launched. The recoil is problematic because it can cause vibrations in the ground that may interfere with the sensor.
U.S. Pat. No. 4,867,266 to Martin teaches a sequential fired seismic energy apparatus for slanted bore holes. Martin teaches that either a vertical bore hole or a slanted bore hole at a 45° angle is first created. After the bore hole is created, an elongated tube that is made of stiff material, such as plastic, is placed into the bore hole when sequential fired seismic energy is desired.
Other methods and apparatuses have been devised which attempt to prevent fluids or water from entering the barrel of a seismic gun. For example, U.S. Pat. No. 4,324,310 to Wener et al. teaches a seismic gun barrel assembly that holds one or more explosive energy sources. Additionally, the barrel comprises seals, such as “O” rings, to provide a water-tight seal to exclude water.
Another method and apparatus that has been devised for the exploration of geographical areas is disclosed in U.S. Pat. No. 5,996,709 to Norris. Norris teaches a system and a portable drill for drilling a shot hole in mixed geologic conditions. Additionally, the apparatus of Norris teaches a shot barrel engaged with the drill to create a shot hole path for directing explosive projectiles against hard rock.
Neither the system nor the methods disclosed in the Martin, Wener and Norris patents remedy the deficiencies of present seismic guns, particularly to non-line-of-sight bore holes, sound suppression and modulating recoil. The water prevention system of Wiener is likewise deficient and fails to cure the deficiencies of the present seismic guns.
Thus, the prior art does not recognize or cure the above deficiencies of present seismic guns. The present invention provides a solution to prior deficiencies associated with curved bore holes, sound suppression, water prevention, and modulating recoil of a seismic gun.